Adjust documentation for git migration.

This fixes most references to the paths:
 llvm.org/svn/
 llvm.org/git/
 llvm.org/viewvc/
 github.com/llvm-mirror/
 github.com/llvm-project/
 reviews.llvm.org/diffusion/

to instead point to https://github.com/llvm/llvm-project.

This is *not* a trivial substitution, because additionally, all the
checkout instructions had to be migrated to instruct users on how to
use the monorepo layout, setting LLVM_ENABLE_PROJECTS instead of
checking out various projects into various subdirectories.

I've attempted to not change any scripts here, only documentation. The
scripts will have to be addressed separately.

Additionally, I've deleted one document which appeared to be outdated
and unneeded:
  lldb/docs/building-with-debug-llvm.txt

Differential Revision: https://reviews.llvm.org/D57330

llvm-svn: 352514
diff --git a/llvm/docs/TestSuiteGuide.md b/llvm/docs/TestSuiteGuide.md
index 0d9bbac..d23b383 100644
--- a/llvm/docs/TestSuiteGuide.md
+++ b/llvm/docs/TestSuiteGuide.md
@@ -27,7 +27,7 @@
 2. Check out the `test-suite` module with:
 
    ```bash
-   % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
+   % git clone https://github.com/llvm/llvm-test-suite.git test-suite
    ```
 
 3. Create a build directory and use CMake to configure the suite. Use the